Gamespy have updated their San Andreas Feature with more information and speculation regarding the game's features, graphics and music. Unfortunately, nothing is revealed that has not been already, but interestingly, they claim that many of the 'exclusive details' featured in print articles from GameInformer and Official Playstation 2 UK Magazine are unconfirmed.
Thanks to Gamespy for using our information in their article, and giving us credit and linkage!

It's also anticipated that CJ will be able to swim through bodies of water -- which then implies that you won't auto-drown or die if your ride beefs it over the edge into a harbor or lake. This would be a most welcome addition. The UK's Official PlayStation 2 Magazine has stated that CJ will be able to escape and swim free of car wrecks, and indeed, that SA will feature specific underwater/swimming missions. There's a good chance to this physical exercise will help CJ shed those extra pounds brought on by eating too much pizza.

(I think if there are going to be swimming and under water missions that submarines are deffinately going to be in the game.) Just remember everyone that i came up with the idea first LOL

Official UK PS2 mag had a world exclusive interview, and they saw the game in action. All the details in that magazine are confimed. Rockstar said that they had already filled one dvd and were onto a second layer. Also it says there won't be a lot of swimming in the game - you can just get out of your car if it falls in a river and swim out (you have a stamina meter).